Big Three Dragons: A z = 7.15 Lyman-break galaxy detected in [O III] 88 μm, [C II] 158 μm, and dust continuum with ALMA
Abstract
We present new ALMA observations and physical properties of a Lyman break galaxy at z = 7.15. Our target, B14-65666, has a bright ultra-violet (UV) absolute magnitude, MUV ≈ -22.4, and has been spectroscopically identified in Lyα with a small rest-frame equivalent width of ≈4 Å. A previous Hubble Space TElescope (HST) image has shown that the target is composed of two spatially separated clumps in the rest-frame UV. With ALMA, we have newly detected spatially resolved [O III] 88 μm, [C II] 158 μm, and their underlying dust continuum emission. In the whole system of B14-65666, the [O III] and [C II] lines have consistent redshifts of 7.1520 ± 0.0003, and the [O III] luminosity, (34.4 ± 4.1) × 108 L⊙, is about three times higher than the [C II] luminosity, (11.0 ± 1.4) × 108 L⊙. With our two continuum flux densities, the dust temperature is constrained to be Td ≈ 50-60 K under the assumption of a dust emissivity index of βd = 2.0-1.5, leading to a large total infrared luminosity of LTIR ≈ 1 × 1012 L⊙. Owing to our high spatial resolution data, we show that the [O III] and [C II] emission can be spatially decomposed into two clumps associated with the two rest-frame UV clumps whose spectra are kinematically separated by ≈200 km s-1. We also find these two clumps have comparable UV, infrared, [O III], and [C II] luminosities. Based on these results, we argue that B14-65666 is a starburst galaxy induced by a major merger. The merger interpretation is also supported by the large specific star formation rate (defined as the star formation rate per unit stellar mass), sSFR = 260^{+119}_{-57}Gyr-1, inferred from our SED fitting. Probably, a strong UV radiation field caused by intense star formation contributes to its high dust temperature and the [O III]-to-[C II] luminosity ratio.
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- August 2019
- DOI:
- 10.1093/pasj/psz049
- arXiv:
- arXiv:1806.00486
- Bibcode:
- 2019PASJ...71...71H
- Keywords:
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- galaxies: formation;
- galaxies: high-redshift;
- galaxies: ISM;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 24 pages, 13 figures, 9 tables. Accepted for publication in PASJ. In addition to the dust continuum detection in ALMA Band 6 reported in the original manuscript, we newly report the dust continuum detection in ALMA Band 8 based on our new ALMA Cycle 5 observations